The present invention is relates to a magnetic sensor apparatus for detecting magnetic field strengths. More specifically, the present invention is directed to a magnetic sensor apparatus capable of directly producing digital sensor data from a magnetic sensor element without using an A/D converter.
Conventionally, Hall-effect elements for detecting magnetic field strengths are used as magnetic sensor elements. When a magnetic field is applied to a Hall-effect element, this element outputs a voltage in an analog value in response to the strength of the applied magnetic field. Since a characteristic of this Hall-effect element varies, the sensitivities, offset, temperature characteristics of this Hall-effect element are required to be adjusted by a sensor signal processing circuit. In other words, in this sensor signal processing circuit, an analog voltage output from the Hall-effect element is adjusted by either an analog circuit or a digital circuit, so that such a sensor output is produced after its offset and temperature characteristic have been corrected.
In this case, in order that the analog voltage output of the Hall-effect element is adjusted by the digital circuit, this analog voltage output must be converted into a digital voltage signal by employing an A/D converter. Also, even in a case that the adjustments of the analog voltage output from the Hall-effect element are carried out by employing analog circuits, an electronic control apparatus is operated in a substantially digital manner by which the sensor signal of this Hall-effect element is finally acquired and then is processed by a predetermined process operation. As a consequence, this sensor signal must be eventually converted to a digital signal by the A/D converter. Since the A/D converter must be built in the sensor signal processing circuit, manufacturing cost of the sensor signal processing circuit increases.
The present invention has been made to solve the above drawbacks, and has an object to provide a magnetic sensor apparatus capable of directly producing a digital sensor value from a magnetic sensor element without employing an A/D converter.
According to the present invention, a plurality of semiconductor magnetic sensors is connected in a ring form to provide a ring circuit in a magnetic sensor apparatus. Each of the semiconductor magnetic sensors deflects carriers flowing through the channel region by using the Hall-effect, the amount of the carriers which flow through the separated drain region, namely, the current value, changes in correspondence with the strength of the magnetic field to be detected.
In the ring circuit, one of separated drain regions of a pre-staged semiconductor magnetic sensor, which is connected to a power supply, is connected the gate electrode of a post-staged semiconductor magnetic sensor. As a consequence, when the pre-staged semiconductor magnetic sensor is brought into the ON-state, namely when a voltage is applied to the gate electrode of the pre-staged semiconductor magnetic sensor, a current starts to flow between the drain region and the source region. As a result, since the potentials of the separated drain regions are approximated from the power supply potential to the ground potential, no drive voltage is applied to the gate electrode of the post-staged semiconductor magnetic sensor, so that this post-staged semiconductor magnetic sensor is brought into the OFF-state.
Each of the semiconductor magnetic sensors which constitute the ring circuit may function as an inverting circuit. If a level of an inputted voltage is a high level (Hi-level), then a voltage having a low level (Lo-level) is outputted. On the other hand, if a voltage having a Lo-level is conversely inputted, then a voltage having a Hi-level is outputted.
In this case, when a drive voltage is applied to the gate electrode of a certain semiconductor magnetic sensor, since carriers may flow through the channel region of this semiconductor magnetic sensor, a current may flow between the source and the drain of this semiconductor magnetic sensor. At this time, the current values of the separated drain regions changes in response to the strength of the magnetic field to be detected. On the other hand, in the post-staged semiconductor magnetic sensor, the power supply voltage is being applied to the gate electrode thereof just before the drive voltage is applied to the gate electrode of the pre-staged semiconductor magnetic sensor.
Under this condition, if the current starts to flow through the pre-staged semiconductor magnetic sensor, then delay is caused until the potential of this gate electrode is lowered due to stray capacitance of the gate electrode and of the wiring line which connects the separated drain electrodes to the gate electrode. This delay time changes in response to a magnitude of such a current which flows through the drain region connected to the ground since the pre-staged semiconductor magnetic sensor is turned on. That is, when the current value flowing through one of the separated drain regions in the pre-staged semiconductor sensor is higher than the current value flowing through the other drain region, the electron charges stored in the stray capacitance can be quickly discharged, so that the delay time until the post-staged semiconductor magnetic sensor is turned off may be shortened. On the other hand, when the current value flowing through one of the separated drain regions in the pre-staged semiconductor sensor is lower than the current value flowing through the other drain region, the delay time may be prolonged.
As a consequence, the current values flowing through the separated drain regions changes in response to the strength of the magnetic field to be detected, and further, the delay time changes in response to this current value. This delay time is defined after the pre-staged semiconductor magnetic sensor is turned on until the post-staged semiconductor magnetic sensor is turned off. As a result, the strength of the magnetic field to be detected may be detected based upon this delay time.
Since a plurality of semiconductor sensors forms the ring circuit, the delay time may be obtained from propagation conditions of such a pulse signal during a predetermined time period, which is inverted from the Hi-level to the Lo-level, or from the Lo-level to the Hi-level by each of the semiconductor magnetic sensors employed in the ring circuit.
As a consequence, the propagation condition of the pulse signal in the ring circuit for a predetermined time period is detected. As this propagation condition, it may be expressed as digital data from a total ringing time of the pulse signal in the ring circuit, and a total number of semiconductor magnetic sensors which have executed the inverting operations during a predetermined time period. As a consequence, since a plurality of semiconductor magnetic sensors are connected to each other in the ring shape, the digital data produced in response to the strength of the magnetic field to be detected can be obtained without employing the A/D converter.